Cardiac arrest is a life-threatening medical condition that may be treated with external defibrillation. External defibrillation includes applying electrodes to the patient's chest and delivering an electric shock to the patient to depolarize the patient's heart and restore normal sinus rhythm. The chance that a patient's heart can be successfully defibrillated increases significantly if a defibrillation pulse is applied quickly.
Until recently, only individuals such as paramedics, emergency medical technicians, police officers, and others trained in defibrillation techniques used defibrillators. However, in a cardiac arrest event the patient's need is urgent and the patient cannot wait for trained personnel to arrive. In recognition of the need for prompt treatment, automated external defibrillators (AEDs) are becoming more commonplace, and are available in venues such as health clubs, auditoriums, and most recently private homes. Ready availability of AEDs may mean that patients can get needed treatment promptly, and need not wait for emergency personnel to arrive. As a result, more lives may be saved.
An AED may be used infrequently, whether it is placed in a commercial setting or in a private household. The battery within the AED will gradually discharge because of self-discharge and automated self-testing that is conducted on a periodic basis (daily, weekly, etc.). Since the AED is used infrequently, the battery status may not be checked on a regular basis. As a result, when the AED is brought into use, possibly years after purchase, the battery may not have sufficient energy to allow the AED to perform its intended function (ECG analysis and defibrillation).
As part of ordinary maintenance procedures, AEDs deployed may be periodically checked. Typically in public venues a person, such as a security worker, may be assigned to make an inspection of each AED and confirm that the device is operational. The inspection may be relatively simple, because many AEDs perform one or more automatic self-diagnostic routines and provide one or more status indications that the device is operational or in need of service.
As part of the inspection, the responsible person regularly reviews each AED and checks its associated status indicators. The responsible person may also be required to prepare and maintain records showing that the inspections have been performed, as well as log the status and repair history of the AEDs. However, in a public venue having several AEDs, the cost of inspection may be significant. Further, a deployed AED may be unprepared to provide defibrillation therapy if the responsible person fails to make an inspection, forgets to make an inspection, or makes an inspection error.
These problems are exacerbated in a private venue or a household where an AED may be used even more infrequently, and thus the AED may have a larger chance of not being properly inspected. It may be more likely in a private venue or a household the user will forget about the AED due to the long time periods between AED uses. Thus, there is a greater chance in these private settings the AED battery will not be properly charged and that the user may not have purchased a replacement battery.
Generally, disposable batteries power most AEDs. There are presently AEDs, which have an option for using rechargeable batteries. In these AEDs, removing them from the unit and connecting an AC-powered charger charge the batteries. A problem associated with using these AEDs using AC power is that the leakage current to the patient must be kept below the limits set by industry standards, which require the use of large isolation components, typically transformers. These devices, while they have proved effective as AEDs, are also larger and heavier and thus make the AEDs more difficult to use and transport.
Another challenge with defibrillators is providing for user safety from the high voltages generated by the AED. In some AEDs, safety is provided by having no exposed, user-accessible contacts other than the defibrillation electrodes (pads). However, these AEDs utilize removable batteries that are inserted into the AED and removed when the battery is depleted. Having a traditional battery charger that is powered by the AC line power typically has user-accessible contacts that would have to be electrically isolated within the AED. This isolation would increase the cost and size of the AED.